The present invention relates generally to improvements in cryogenic storage tanks, and more particularly to a novel tank structure for storage of a cryogenic liquid including means for controlled positive expulsion of the cryogenic liquid therefrom.
In low gravity or negative gravity fields, cryogenic liquids need positive expulsion for controlled flow from the vessels within which they are stored. Typical positive expulsion devices include rubber diaphragms or bladders or metallic bellows. Rubber and other elastomeric materials are not normally suitable for use in cryogenic storage vessel construction where they contact the very low temperatures characteristic of a cryogenic liquid, since they are embrittled at cryogenic temperatures and many are not compatible with such oxidizers as liquid fluorine or nitrogen trifluoride. Also, typical cryogenic storage tanks presently used aboard space-launched vehicles comprise heavy double-walled dewar-type vacuum vessels which require boil-off to relieve pressure and to maintain cooling. Existing tank structures including metallic bellows are likewise undesirably heavy.
The present invention provides a novel tank structure configured for storing a cryogenic liquid either for terrestrial operation or for use aboard a space vehicle and including means for the controlled positive expulsion of the contained cryogenic liquid in any gravity environment, including the influence of normal gravity, or a zero gravity environment, or the excessive g forces (positive or negative) that may be characteristic of an accelerating coordinate system of an operating spacecraft. The structure of the tank of the present invention comprises a thin metallic bladder providing primary containment for the cryogenic liquid. A high-pressure containment shell surrounds the bladder and is in turn enclosed within a thin metallic shell. The high-pressure containment shell is centered within the metallic shell in a spaced relationship by a plurality of struts or tension straps to define a space within which a cryogenic coolant may be maintained for primary insulative purposes. The outer surface of the metallic shell may be covered with a layer of foam to provide secondary insulation. A source of pressurized gas is operatively connected to the high pressure containment shell for controllably exerting gas pressure on the exterior surface of the bladder, and thereby controllably collapsing the bladder to provide controlled flow of the cryogenic liquid therefrom. As compared to existing tank structures, the cryogenic storage tank of the present invention minimizes the space occupied by a given volume of contained cryogenic liquid, minimizes any amount of cryogenic coolant which may be required as primary insulation, minimizes the amount of contained cryogenic liquid wasted as a result of boiloff, maximizes the strength of the tank structure, and minimizes any weight penalty associated with its inclusion within a vehicle.
It is, therefore, a principal object of the present invention to provide an improved tank for storing or transporting cryogenic liquids.
It is a further object of the invention to provide a cryogenic tank having positive expulsion capability for supplying a cryogenic liquid therefrom.
It is a further object of the invention to provide a cryogenic tank for supplying cryogenic liquids under zero or other abnormal gravity environments.
These and other objects of the present invention will become apparent as the detailed description of certain representative embodiments thereof proceeds.